1. Field of the Invention
The present invention relates to a slurry which undergoes exothermic reaction by combustion synthesis when ignited, and methods for the use thereof in joining metallic or ceramic surfaces or for coating metallic, ceramic and refractory surfaces. Although not so limited, slurries of the invention have particular utility in joining stainless steel, aluminum, carbon steel and copper workpieces and in forming coatings on porous silica or aluminum oxide substrates which resist chemical attack, ingress and attack by molten alloys having high melting temperatures.
2. Prior Art
Joints between metal pieces are conventionally formed by welding or brazing, by means of a wide variety of techniques using an oxyacetylene torch, or the like. Brazing compositions for joining metal pieces by fusion are also well known. To the best of applicant's knowledge there have been no suggestions in the prior art to use a slurry for joining metallic pieces, the constituents of which are so selected and proportioned as to undergo exothermic reaction by combustion synthesis when ignited, thereby welding the metal pieces together.
Ceramic materials such as silica, alumina, zirconia and the like are used for containing molten metals, in furnaces for melting metals, in armor for missiles and the like, as infrared sensors, in electronic packaging, in engine materials, and in related applications. Such ceramic materials are frequently porous because they are made from powders which are sintered. Although porosity may be beneficial in imparting low density and specific toughness, porosity is detrimental from the standpoint of chemical attack, ingress into the ceramic or refractory material and resistance against attack by molten alloys at high temperature. Expensive fabrication is necessary to obtain a ceramic material of the above type in a fully densified condition. The prior art has resorted to coating ceramic surfaces in order to eliminate ingress or diffusion of material such as molten metal into the ceramic. No generally suitable technique is known to applicant to solve the problems inherent in coating ceramic or refractory surfaces.
Despite the existence of a wide variety of welding and brazing techniques and compositions, and despite the prior art suggestions for coating porous ceramic or refractory surfaces, a genuine need exists for alternative compositions and methods for joining metallic or ceramic surfaces or for coating metallic, ceramic and refractory surfaces.